Chemical analysis of the Genesis Rock indicated it is an anorthosite, composed mostly of a type of plagioclasefeldspar known as anorthite. The rock was formed in the early stages of the solar system, at least 4 billion years ago.[1] It was recovered in a crater of the Moon, near other rocks of its kind.

It was originally thought they had found a piece of the Moon's primordial crust, but later analysis initially showed that the rock was only 4.1 ± 0.1 billion years old, which is younger than the Moon itself; and was formed after the Moon's crust solidified. But it was still an extremely old sample, and was from the Pre-Nectarian. Dating of pyroxenes from other anorthosite samples gave a samarium-neodymium age of crystallization of 4.46 billion years.[2]